Arc chute plates for air curcuit breaker

ABSTRACT

The arc chute of a low-voltage air magnetic-type electric circuit breaker comprising a stack of spaced-apart porous metal plates made of fiber metal. All of the plates are impregnated or coated with ceramic insulating material at least on their lower regions.

United States Patent Armitage et al.

[ Feb. 8, 1972 [54] ARC CHUTE PLATES FOR AIR CURCUIT BREAKER [72]Inventors: Charles H. Armitage, Wauwatosa, Wis; Henry L. Peek,Wellesley; Herbert M. Pflanz, Westwood, both of Mass.

[73] Assignee: Allis-Chalmers Manufacturing Company,

Milwaukee, Wis.

[22] Filed: Dec. 8, 1970 [21] App1.No.: 1,443

[52] U5. Cl. ..200/l44 R, 200/147 [51 Int. Cl. .Q H0lh 33/08 [58] FieldofSearch ..200/144, 147,147 B [56] References Cited UNITED STATESPATENTS 2,911,505 11/1959 Legg et a1 ..200/144 C I FOREIGN PATENTS ORAPPLICATIONS 1,334,841 7/1963 France ..200/I47 B Priniary ExaminerRobertS. Macon Attorney-Thomas F. Kirby, Lee H. Kaiser and Robert B. BensonABSIRAC'I The are chute of a low-voltage air magnetic-type electriccircuit breaker comprising a stack of spaced-apart porous metal platesmade of fiber metaL All of the plates are impregnated or coated withceramic insulating material at least on their lower regions.

2 Claims, 4 Drawing Figures ARC CIIUTE PLATES FOR AIR CURCUIT BREAKERBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to are chutes for electric circuit breakers whichemploy a plurality of spaced-apart plates to divide up an are intosmaller segments during extinguishment and, particularly, to metalplates which are coated with are resistant insulating material.

2. Description of the Prior Art Some circuit breakers for interruptingalternating current use an arc chute having a stack of spaced-apartplates of magnetizable metal located between a pair of arc runners andadjacent the circuit breaker contacts. Such plates divide the long arebetween the arc runners into a multiplicity of series connected smallerarcs and cause them to move through the arc chute; the object being toraise the reigrrition voltage. Extinguishment is aided by the cooling ofthe small arcs in contact with the metal plates and by the turbulencepresent as the arcs move through the space between the plates.

Plates made of solid insulating material have been interspersed betweenthe metal plates to aid arc extinguishment by providing a more tortuouspath for the are. US. Pat. No. 2,91 1,505 issued Nov. 3, 1959 to D. Legget al. teaches an arrangement wherein all plates in the arc chute aremade of solid sheets of magnetizable metal and completely coated withtwo different types of insulating material. While the latter arrangementachieves the desired electrical result, it involves costly andcomplicated arc chutes and requires plates of greater thickness than maybe desirable for certain applications. It is desirable, therefore, toprovide new and improved arc chute plates wherein the plates areconstructed of fiber metals which are partially or completely coated orimpregnated with refractory insulating material so as to improve theextinguishing ability of the arc chute and provide improved platestherefor.

SUMMARY OF THE INVENTION The present invention contemplates an arc chutewherein a stack of plurality of spaced-apart plates are disposed betweena pair of arc runners. In accordance with the present invention it isproposed to provide plates made of fiber metal, preferably magnetizable,and to coat all or part of the metal plates with a single coat or layerof arc resistance refractory insulating material, such as ceramic.

OBJECT S OF THE INVENTION It is an object of the present invention toprovide an improved arc chute which employs plates made of fiber metaland fully or partially coated with refractory insulating materia]Another object is to provide an arc chute which employs such plateswhich are of uniform size and configuration so as to provide an arcchute which has advantages of metal and insulating plates incombination.

Another object is to provide an arc chute plate of the aforesaidcharacter which are electrically effective, mechanically strong andresistant to damage caused by thermal expansron.

Another object is to provide an arc chute which avoids close tolerancefitting between dissimilar constitutent elements to effect efficient arcextinguishment.

Anofl'rer object is to provide plates which are strong, .damageresistant, and relatively thinner than other coated plates.

Another object is to provide an arc chute and plates of the aforesaidcharacter which are economical to fabricate and re liable in use.

Other objects and advantages will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing illustratespreferred embodiments of the invention but it is to be understood thatthe embodiments illustrated are susceptible of modifications withrespect to details thereof without departing from the scope of theappended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section, of a portion of acircuit breaker arc chute incorporating the present invention;

FIG. 2 is a view taken along line II-II of FIG. 1;

FIG. 3 is a cross-sectional view taken along line IIIIII of FIG. 2; and

FIG. 4 is an elevational view of an arc plate in accordance with anotherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 ofthe drawing, the numerals l0 and 12 designate stationary and movablecontacts, respectively, of an electric circuit breaker which separate toestablish an arc. An arc chute 14 is associated with contacts 10 and 12and comprises a pair of spaced-apart sidewalls l6 and 18 which are madeof electrical insulating material such as ceramic, insulating fiber, orthe like. It is to be understood that the sidewalls 16 and 18 are mirrorimages of each other and are formed with suitable projections andrecesses to support various components therein when the sidewalls arefastened together. The sidewalls l6 and 18 define an arcing chamber 20in the lower portion of arc chute 14 wherein stationary contact 10 andmovable contact 12 are disposed. Stationary contact 10 is rigidlymounted with respect to are chute l4 and is located at one end ofchamber 20. Stationary contact 10 is electrically connected to a firststationary electrically conductive arc runner 22 which is also locatedat the aforesaid one end of chamber 20 of arc chute l4. Movable contact12 is pivotally mounted for clockwise and counterclocklise movement(with respect to FIG. 1) within chamber 20 of arc chute 14 into and outof engagement, respectively, with stationary contact 10. When movablecontact 12 is moved counterclockwise it comes into proximity with asecond stationary electrically conductive arc runner 24 which is locatedat the other end of chamber 20 of arc chute 14 and spaced apart from arcrunner 22. During circuit interruption, an are established between thecontacts 10 and 12 is transferred therefrom so that it becomesestablished between the are runners 22 and 24 and travels upwardthereon, as hereinafter explained.

Arc chute 14 comprises a stack 26 of plates which span the sidewalls l6and 18 above chamber 20 and are disposed in spaced-apart relationshipbetween the arc runners 22 and 24. One end of the stack of plates 26 iscloser to the contacts than the other end. Arc chute 14 is provided withmeans for cooling the exhaust gases expelled from the top of the stackof plates 26. Such means take the form of hollow baffle members 42 whichare supported by perforated insulating members 44.

All plates in stack 26 may be are of the same configuration and size.The plates in stack 26 are arranged with respect to each other so thatthe upper edges of all plates (the edges most remote from the contacts)terminate in a first common horizontal plane. The upper edges of the arcrunners 22 and 24 also terminate in or below the aforesaid first plane.The lower edges of all plates in stack 26 (the edges nearest thecontacts) terminate in a second common horizontal plane. The plates instack 26 are held in position by entrapment in grooves 30 provided inthe sidewalls l6 and 18. Each plate in stack 26 is provided with atriangular slot 28 at its lower edge to guide the arc into the stack ofplates during operation of the arc chute.

The spacing between each plate and an adjacent plate in the stack isregular and is the same as the spacing between the arc runners 22 and 24and the plates adjacent thereto.

In accordance with the invention each plate 32 in stack 26 comprises asheet 34 of magnetizable metal such as steel which is in the form offiber metal. In accordance with the embodiment of the invention shown inFIGS. 1 and 2, the metal in each plate is entirely coated with arcresistant insulating material 36, such as ceramic, which has beensuitably fired to harden it and to cause it to bond securely to themetal. Bonding is improved by the fact that the surface of the fibermetal is irregular and provided with many interstices. The fiber metalportion 34 of plates 32 is somewhat more resilient or flexible than asolid metal plate would be.- Accordingly, when it is bonded to theceramic material a greater mismatch in thermal expansion characteristicsis permissible between the fiber metal and the ceramic than would bethecase with a solid sheet of the same metal. However, it is desirableto select magnetizable fiber metal which has a coefiicient of thermalexpansion which is as close as practical to that of the ceramic materialwhich is chosen to further reduce the possibility of cracking theceramic when the plates are subjected to high temperatures during andafter arcing. The ceramic may be applied in any conventional manner asby dipping, spraying or painting prior tofiring. Since only a singlecoating of ceramic is required and since such coating is relativelythin, i.e., on the order of a few thousands of an inch thick, the totalthickness of each plate 32 and the overall dimensions of the arc chute14 are not substantially greater than they would be if uncoated metalplates were used. 7

A plate constructed as above described, therefore, combines the magneticcharacteristics of the conventional ferrous metal arc plate with theadvantages of conventional arc chute plates made of solid insulatingmaterial. Furthermore, plate 32 is an improvement over are chute platesof solid metal coat with an insulating coating because of the thermalcharacteristics and behavior described above and because of the smallerdimensions resulting from the sue of a single thin insulating coatingwhich is firmly bonded to the fiber metal. Furthermore, in a plate usinga fiber metal it is possible through careful selection of the fibermaterial and orientation of the fiber to amplify and capitalize on themagnetic characteristics of the metal to achieve improved arc chuteperforrnance.

Arc chute 14 operates as follows: Assume that the contacts 10 and 12 ofthe circuit breaker are closed and the current is flowing therethrough.As movable contact 12 is moved counterclockwise (with respect to FIG. 1)from closed toward open position, an arc appears between contacts 10 and12. Because of the electromagnetic forces present, the terminal point ofthe are on contact 10 transfers to are runner 22 and the terminal pointof the arc on contact 12 moves to the extreme tip of contact 12. The arcforms an inverted U-shape with its highest point entering within theslots 28 in the stack of plates 26 at the end of the stack nearest arcrunner 22. As movable contact 12 moves closer to are runner 24, the arcterminal on the former transfers to the latter, and an elongated arc isestablished between the arc runners 22 and 24. As the elongated arcmoves up through and past the slots 28 in the stack 26, it is dividedinto a plurality of series related small arcs. The small arcs tend tomove upward through the stack at a relatively uniform rate. In theembodiment shown, the arcing forces and are byproducts are most numerousat the end of the arc chute nearest stationary contact 10 (i.e., thepoint of arc initiation). Since the arcing forces and byproducts areless effective at the upper end of the stack the insulated platesthereat are sufficient to reduce the likelihood of flashover across thetop of the plates. However, these factors are offset to some extentbecause during interruption of an arc, the hot gas from arcing is ventedthrough the arc chute in an upward direction.

As a result of cool air or gas entering from the bottom a temperaturegradient exists along the vertical path of the arc chute. The hot gas inthe upper zone has a lower breakdown voltage than the cooler gas in thelower zone.

As previously mentioned, it is desirable to retain as many 7 metalplates as possible in the stack in order to increase the arc voltage.The use of coated metal plates permits this. Exhaust products from thearc are cooled and condensed by means of the baffles 42 before beingexpelled from the arc chute.

FIG. 4 shows another embodiment of arc chute plate 40 in accordance withthe present invention. Arc chute plate 40 is understood to be similar toarc chute plate 32 hereinbefore described except that its uppermostportion 42 is not provided with a ceramic insulating material. Byomitting the ceramic coating on the top or upper end of plate 40 anefficient cooling surface is obtained which permits more rapid coolingof arc chute 14. Of course, the overall dimensions of plate 40 and thearc chute must be such that the insulating coating is not eliminated inregions where arc reignition might occur.

Plate 40 is understood to be arranged and operates in substantially thesame manner as the plates 32 hereinbefore described, except as regardsits cooling characteristics.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An arc chute plate for use in an electric circuit breaker whichemploys at least one plate located between spaced apart arc runners,

said plate comprising a sheet of magnetizable fiber metal,

said sheet of fiber metal comprising fibers which are oriented toamplify the magnetic characteristics of said plate,

said sheet having front and rear surfaces and side, top and bottom edgesurfaces,

and a single layer of ceramic material bonded by firing directly atleast to the lower half of said front and rear surfaces, to the lowerhalf of said side edge surfaces, and to said bottom edge surface.

2. A plate according to claim 1 wherein said insulating material coversall of said surfaces of said sheet.

1. An arc chute plate for use in an electric circuit breaker whichemploys at least one plate located between spaced apart arc runners,said plate comprising a sheet of magnetizable fiber metal, said sheet offiber metal comprising fibers which are oriented to amplify the magneticcharacteristics of said plate, said sheet having front and rear surfacesand side, top and bottom edge surfaces, and a single layer of ceramicmaterial bonded by firing directly at least to the lower half of saidfront and rear surfaces, to the lower half of said side edge surfaces,and to said bottom edge surface.
 2. A plate according to claim 1 whereinsaid insulating material covers all of said surfaces of said sheet.